Liquid treatment plant and process, particularly for waste water

ABSTRACT

A treatment process and plant particularly adapted to be embodied in a compact package unit designed in particular to efficiently remove phosphorus and other pollutants from waste water. A treatment process wherein lime or other chemical coagulant is intimately mixed with an influent solution to coagulate the solute and to flocculate the suspended particles into a flocculation chamber wherein the mixture is subjected to raising through a field of suspended particles and to reseeding with deposited particles to encourage the flocculation. Thereafter, the mixture is caused to pass through curtains of falling floc and between sedimentation trays to deposit the particles. The unit is constructed and arranged to produce gravity flow serially and at predetermined individual velocities through the successive stages of the process to optimize the flocculation and deposition conditions therein.

United States Patent 1 1 Chatfield Dec. 18, 1973 LIQUID TREATMENT PLANTAND PROCESS, PARTICULARLY FOR WASTE WATER AIRLIFT PUMP STIRRER 2 SLUDGEr 20 ,9

PERNATANT l3 SLUDGE 22 EFF LUENT p14 CHLORINE CONTACT ,kcHAMBERCONTAINER J Primary ExaminerFrank A. Spear, Jr. AssistantExaminer-Benoit Castel Attorney--Arnold B. Christen et al.

[57] ABSTRACT A treatment process and plant particularly adapted to beembodied in a compact package unit designed in particular to efficientlyremove phosphorus and other pollutants from waste water. A treatmentprocess wherein lime or other chemical coagulant is intimately mixedwith an influent solution to coagulate the solute and to flocculate thesuspended particles into a flocculation chamber wherein the mixture issubjected to raising through a field of suspended particles and toreseeding with deposited particles to encourage the flocculation.Thereafter, the mixture is caused to pass through curtains of fallingfloc and between sedimentation trays to deposit the particles. The unitis constructed and arranged to produce gravity flow serially and atpredetermined individual velocities through the successive stages of theprocess to optimize the floccu lation and deposition conditions therein.

4 Claims, 3 Drawing Figures LIME I6 LL- 1I1FLUENT 24 CHLORINE METERINGUNIT -SEDIMENTATION TRAYS PATENTEUBEB 18 1915 3.779.910

SHEET 20F 2 1 FIG. 3 27 25 LIQUID TREATMENT PLANT AND PROCESS,PARTICULARLY FOR WASTE WATER This invention relates to purifyingtreatment and unit for a solution and more particularly, to a wastewater treatment process and to a plant or unit therefor.

' Many factors or principles favorably influence the efficiency of thetreatment of waste water. Such favorable factors include appropriateresidence times in the mixing and flocculation zones or chambers,thorough mixing of the coagulating chemical with the waste water, thepassing of the waste water through fields, beds or blankets of suspendedparticles, reseeding deposited sludge particles into the flocculationzone or chamber, and passing the waste water through falling floc andbetween sedimentation trays. lt is found that the same factors alsoapply to the purifying of other solutions.

The waste water treatment plants of the type using chemical coagulationwhich have been proposed and operated so far, do not draw maximumadvantages from the above factors or principles. The known waste watertreatment processes and plants are essentially constructed to use onlysome but not all the above principles. Nobody so far has been able toembody the above principles in a single operative unit to obtain maximumbenefits from the available know-how in this field.

It is a general object of the present invention to combine into a singleand compact unit, the abovementioned factors or principles to optimizethe purifying treatment efficiency.

It is another general object of the invention to provide a singlecompact unit to effect purifying treatment of a solution and inparticular waste water.

It is a further general object of the invention to provide a compactpackage purifying unit which has .a minimum number of submerged movableparts and which is of simple construction, maintenance and operation.

It is further general object of the invention to provide a purifyingtreatment unit and process including various steps in which theindividual throughflow velocities and the residence times of the wastewater or other solution are predetermined to give the best possibleresults.

It is a further general object of the invention to provide a waste watertreatment unit and process particularly adapted to remove phosphorusfrom waste water.

It is another general object of the invention to provide a purifyingtreatment process and unit wherein the throughflow is produced by thegravity action.

It is a more specific object of the invention to provide a purifyingtreatment unit or plant including compactly nested enclosures andpartitions suitably arranged relative to each other to form anup-and-down tortuous flow path forming the desired treatment chambers orzones.

It is a further specific object of the invention to provide a wastewater treatment unit having chambers suitably arranged and shaped toproduce the desired individual velocities of flow and residence times ofthe waste water therein.

The invention will now be defined with reference to the accompanyingdrawings which schematically illustrate, by way of example only, a wastewater treatment unit, according to a preferred embodiment of theinvention.

FIG. 1 is a cross sectional elevation view taken through the centralvertical axis of the unit;

FIG. 2 is a plan section view taken along line 2-2 in FIG. 1;

FIG. 3 is a fragmentary cross sectional elevational view taken alongline 3-3 in FIG. I;

The preferred embodiment of the invention which will now be described indetail is particularly applied to the treatment of waste water but thesame treatment unit and process may also be used for the purification ofother solutions with or without the use of a chemical coagulant.

When certain chemicals, such as lime and ferric chloride, are added tothe waste water, they coagulate the soluble phosphorus to form insolublechemical compounds. Onto the particles formed by this chemical action,other substances in the waste' water flocculate. These include the BODor biological oxygen demand, and the COD or chemical oxygen demand.Removal of the BOD, COD and phosphorus from the waste water is then afunction of removing the flocculated substances. In order to achievehigh removal efficiencies, the proposed process includes special stepsto ensure effective mixing adequate flocculation, and efficientsedimentation, as will be explained in detail later after the followingdescription of the illustrated waste water treatment unit.

The illustrated compact package unit includes an outside enclosure 1 ofpreferably cylindrical shape enclosing basically three interiorenclosures 2, 3 and 4 nested one within the other as illustrated anddefined hereinafter. The enclosure 2 has a sidewall enclosing aflocculation chamber and including an open-ended downwardly taperingbottom conical portion 5, an open-ended upwardly tapering top conicalportion 6 fixed end to end onto said bottom conical portion 5, and anupwardly diverging conical partition 7. The enclosure 3 includes afunnel shaped sidewall having a top hopper portion 8 and a dependingdischarging tube portion 9 extending near the bottom of the flocculationchamber defined by the enclosure 2. The enclosure 4 has a sidewallforming a downwardly tapering portion 10 surrounding the bottom conicalportion 5 in spaced apart relationship therewith and has a closed bottomend to form a sludge collector, as will be better explained later. Theupper end of the enclosure 4 diverges upwardly and contains a pluralityof sedimentation trays ll of truncated conical shape nested in radiallyspaced apart relationship. It must be noted that the upwardly divergingconical partition 7 extends intermediate the innermost sedimentationtray 11 and the top hopper portion 8 to define an extension 12 of theflocculation chamber and a downflow passage 13 leading to the lower endof the sedimentation trays 11. An upright baffle plate 14 is fixedagainst the interior surface of the outside enclosure 1 and forms anupward flow passage which is opened at the bottom into the contactchamber and which forms an overflow 15 at the top for the treatedeffluent.

A chemical and waste water influent supply pipe 16, as schematicallyillustrated in FIG. 1, is arranged to supply waste water and a meteredquantity of a coagulating chemical, in any well known manner, into themixing chamber defined by the top conical hopper portion 8.

A stirrer including an impeller 17, a drive shaft 18, and a motor 19 isprovided to adequately mix the coagulant with the waste water influent.The impeller 17 is arranged to leave a predetermined restricted passagetherearound into the mixing chamber and is rotated in a direction toupwardly impel or lift the waste water influent and chemical to retardor counter the normal downward flow thereof whereby to attain apredetermined residence time and mixing of the waste water into themixing chamber.

The deposited sludge at the bottom of the downwardly tapering portion islifted upwardly into a pipe 20 by an ar lift or any othe suitable pumpnot sown but as known in the art. The sludge is accumulated into asludge container 21 where the supernatant thereof is allowed to overflowinto the recirculation pipe 22 and the outlet jets 23. The latter arearranged adjacent the upper part of the bottom conical portion 5 toproduce reseeding, recirculation, and gentle tumbling and mixing ofsludge particles therein.

A chlorine supply unit 24 of any suitable type is provided to supplymetered quantity of chlorine, for instance sodium hyporchlorite, toeffect bacterial treatment.

into the contact chamber, there are arranged a limited number ofvertically spaced apart horizontal baffles 25 defining superposedhorizontal annular spaces. A vertical partition 26 extends between eachpair of adjacent horizontal baffles 25. A hole or aperture 27 isprovided through each horizontal baffle 25 adjacent the verticalpartition 26. The holes or apertures 27 are staggered on opposites sidesof the vertical partitions 26 from one baffle 25 to the other wherebythe clarified waste water will enter into each annular space on one sideof the corresponding partition, will flow circumferentially thereintoand will exit thereof on the other side of the same vertical partition.

The unit described and illustrated is operated by supplying waste waterinfluent and the chemical coagulant into the mixing chamber formed bythe top hopper portion 8. As aforementioned, the rotating impeller 17lifts the wastewater and entrained chemical and thereby limits thedownward flow of the latter which under the action of gravity flowsdownwardly around the impeller. There results an increased circulationand therefore mixing of the coagulant with the waste water and anextended residence time of the mixture in the mixing zone or chamber.Researchers have emphasized the need for an extended period of vigorousstirring prior to the flocculation stage. The process according to thepresent invention therefore includes a carefully designed mixing chamberand mixer so arranged that all the influent is adequately mixed for therequired period of residence time and also so arranged that no shortcircuiting of the flow occurs.

The mixed coagulant and waste water, hereinafter called the waste watermixture, flows downwardly through the discharge tube portion 9 and exitsthere from adjacent the lower part of the bottom conical portion 5.There is little turbulence into the lower part of the conical portion 5,and the flocculation with appropriate upward flow velocity of the wastewater mixture causes the formation of a field or blanket of suspendedfloc or particles through which the mixture rises resulting in an upwardflow of partly clarified waste water mixture and a downward flow ofheavier particles and a deposition of sludge at the bottom of thedownwardly tapering portion 10.

As explained above, a pump removes the deposited sludge and accumulatesthe same into the sludge container 21 from which supernatant overflowsand is recirculated into the waste water mixture by the outlets 23. Thefloc or particles in the supernatant assisted by the turbulence orcirculation produced by the outlet jets 23, enhance flocculation of thefree particles remaining suspended in the partly clarified waste watermixture. As the latter flows further upwardly, a second field or blanketof particles forms into the extension 12 of the flocculation chamber andthere results a second clarifying stage or step.

The clarified waste water mixture thereafter flows downwardly throughthe passage 13 to arrive at the lower end of the nested conicalsedimentation trays 11. The passage of the waste water mixture betweenthe trays 11 results in deposition of particles onto the trays anddripping thereof along and at the lower end of the latter. There resultsthe formation of a curtain or curtains of falling floc into the space atthe bottom end of the trays 11 through which the waste water mixture iscaused to flow before entering between the trays, thereby furtherenhancing the flocculation and the deposition of the floc. The latterfalling or dripping from the lower end of the sedimentation trays 11 arecollected by the downwardly tapering portion 10.

The clarified waste water mixture reaching the upper end of thesedimentation trays is allowed to overflow into the contact chamberwhere chlorine is added in metered quantity by a unit 24 to effectbacterial treatment. The passage defined by the upright baffle 14 allowsoverflow of the treated waste water or effluent after the aforementionedbaffled flow through the contact chamber.

It must be pointed out that in the process according to the invention,flocculation is encouraged to take place, in six separate stages orsteps including the creation of two distinct fields of suspendedparticles through which the flow is caused to pass, the reseeding orrecirculation of deposited sludge into incoming waste water mixture,gentle tumbling or circulation thereof, and causing the flow to passthrough specifically arranged curtains of falling floc before passingbetween the sedimentation trays. It should be noted that the combinationof the above stages into a single unit is rendered possible by providingand arranging internal partitions and enclosures to obtain anup-and-down tortuous flow path and a throughflow under the action ofgravity.

Normally, the removal of phosphate and other particles by a chemicalsuch as lime is progressively increased by increasing the pH. By usingrecirculation of deposited particles, the whole process can be carriedout at a pH substantially less than would otherwise be necessary. Thissaves on the amount of chemical required and may obviate the necessityof restoring the water to lower pH value before discharge.

Having used a chemical coagulant to bring the phosphorus out of solutionin the mixing chamber, and having provided conditions which enhance orencourage the formation of floc, the following step for high efficiencytreatment consists in the removal of these floc particles from the wastewater mixture. The step of raising the waste water through a field orblanket of suspended particles acting as upflow clarifier, produces ahigh efficiency removal of suspended solids. Tray sedimentation furtherassists the upflow clarifier technique for high reliable efficiency.

The final step or stage in the process and unit according to theinvention is chlorination in the contact chamber; satisfactory resultsmay be obtained by careful dosage, proper mixing, suitable residencetime and absence of short-circuited flow conditions.

It should also be noted that the relative cross-' sectional areas of thevarious enclosures or passages for the waste water are predetermined toobtain optimum individual velocities of flow and residence times in thevarious distinct chambers and zones through which the flow is subjectedto any particular step of the treatment process.

As briefly explained hereinbefore, the method and unit of the presentinvention are also adapted for the the purification of other solutionsthan waste water.

What I claim is:

1. A liquid purification process comprising serially flowing liquidcontaining impurities under gravity at predetermined relative velocitiesthrough stages including feeding a chemical coagulant to a waste waterinfluent, stirring the latter with the chemical coagulant therein, intoa flocculation chamber, to counter the normal flow to achieve extendedresidence time and reduced throughflow velocity of the waste watermixture through the mixing stage, tunneling the waste water mixture tothe bottom portion of the flocculation chamber, raising the mixturethrough one field of suspended particles, recirculating deposited sludgeinto the flocculation chamber to enhance flocculation into the latter,by pumping deposited sludge into the flocculation chamber, settlingsludge to produce supernatant, causing sludge supernatant to flow intothe flocculation chamber, and tumbling the waste water mixture, raisingthe mixture through another field of suspended particles, passing themixture through curtains of falling floc and between sedimentation traysfor the deposition of sludge and the formation of a clarified wastewater mixture, chemically treating the latter to obtain satisfactoryflocculation and sludge deposition conditions to produce a purifiedwaste water effluent, and allowing said clarified waste water mixture tooverflow.

2. A liquid purification process comprising serially flowing, undergravity, liquid containing impurities at predetermined relativevelocities through stages including, feeding a chemical coagulant to aliquid influent, mixing the coagulant with the influent thereby forminga liquid mixture into a flocculation chamber, raising the mixturethrough at least one field of suspended particles and recirculatingdeposited sludge into the flocculation chamber by pumping depositedsludge above said flocculation chamber, settling sludge to producesupernatant, causing sludge supernatant to flow into the flocculationchamber, and tumbling the liquid mixture to enhance flocculation intothe flocculation chamber, passing the mixture through curtains offalling floc and between sedimentation trays for the deposition ofsludge and the formation of a clarified mixture, further chemicallytreating the latter, whereby to obtain satisfactory flocculation andsludge deposition conditions to produce a purified effluent, andallowing said clarified mixture to overflow under gravity action.

3. A liquid purification treatment plant comprising a unit including,constructed and arranged for serially flowing a liquid containingimpurities therethrough at predetermined individual velocities, afirstenclosure forming a flocculation chamber, a second enclosureforming a mixing chamber adapted to mix a chemical coagulant andinfluent to form a liquid mixture therewith and arranged to dischargeand to cause raising of the latter into said flocculation chamberthrough a field of suspended particles formed into the latter,recirculating means arranged to recirculate and reseed deposited sludgeparticles into the flocculation chamber whereby to enhance flocculationinto the latter, sedimentation trays nested adjacent said flocculationchamber, a passage means for the liquid mixture extending from saidflocculation chamber to the bottom of said sedimentation trays to causethe liquid mixture from the flocculation chamber to flow throughcurtains of falling floc under said sedimentation trays and upwardlybetween the latter for the deposition of sludge and the formation of aclarified liquid mixture, and a third enclosure forming a contactchamber arranged adjacent said sedimentation trays for treating saidclarified liquid mixture, said contact chamber being provided with anoverflow for the effluent, said second enclosure being provided with asidewall having an upper end portion extending higher than saidoverflow, said sedimentation trays having upper ends which are lowerthen said upper end portion of said sidewall whereby said liquid mixtureis allowed to flow under gravity action from said mixing chamber andover said upper ends, to said overflow, said first and second enclosuresand said sedimentation trays being nested inside said contact chamber,and said first, second and third enclosures having sidewalls constructedand arranged to produce an up-and-down tortuous flow path, said firstenclosure having a sidewall having an openended downwardly taperingbottom conical portion and an openended upwardly tapering top conicalportion, the sidewall of said second enclosure having a funnel shapedefining a conical hopper portion and a depending discharge tube portionextending into said bottom conical portion and opening adjacent thebottom thereof, a fourth enclosure surrounding said first enclosure andbeing conically shaped to form a sludge collector around said bottomconical portion, said sedimentation trays being formed of downwardlytapering truncated conical surfaces nested in radially spaced apartrelationship one within another and relative to said conical hopperportion and above said upwardly tapering top conical portion, an uprightbaffle plate being fixed inside said third enclosure and arranged toform an upward flow passage for said effluent leading from said contactchamber to said overflow, and a partition extending upwardly from theupper end of said top conical portion intermediate said conical hopperportion and said sedimentation trays.

4. A treatment plant for waste water as defined in claim 3, furtherincluding a stirring impeller rotatably mounted into said conical hopperportion and arranged upon rotation to counter downward flowtherethrough; said recirculating means includes a recirculating andtumbling zone into said flocculation chamber, an airlift pump having asuction inlet positioned into the bottom of said fourth enclosure andarranged to suck deposited sludge particles into a sludge containerabove said flocculation chamber and a supernatant discharge pipeconnected to said sludge container and having an outlet extending intosaid circulating and tumbling zone and arranged to feed supernatant intosaid zone to cause recirculation of deposited sludge particles.

2. A liquid purification process comprising serially flowing, undergravity, liquid containing impurities at predetermined relativevelocities through stages including, feeding a chemical coagulant to aliquid influent, mixing the coagulant with the influent thereby forminga liquid mixture into a flocculation chamber, raising the mixturethrough at least one field of suspended particles and recirculatingdeposited sludge into the flocculation chamber by pumping depositedsludge above said flocculation chamber, settling sludge to producesupernatant, causing sludge supernatant to flow into the flocculationchamber, and tumbling the liquid mixture to enhance flocculation intothe flocculation chamber, passing the mixture through curtains offalling floc and between sedimentation trays for the deposition ofsludge and the formation of a clarified mixture, further chemicallytreating the latter, whereby to obtain satisfactory flocculation andsludge deposition conditions to produce a purified effluent, andallowing said clarified mixture to overflow under gravity action.
 3. Aliquid purification treatment plant comprising a unit including,constructed and arranged for serially flowing a liquid containingimpurities therethrough at predetermined individual velocities, a firstenclosure forming a flocculation chamber, a second enclosure forming amixing chamber adapted to mix a chemical coagulant and influent to forma liquid mixture therewith and arranged to discharge and to causeraising of the latter into said flocculation chamber through a field ofsuspended particles formed into the latter, recirculating means arrangedto recirculate and reseed deposited sludge particles into theflocculation chamber whereby to enhance flocculation into the latter,sedimentation trays nested adjacent said flocculation chamber, a passagemeans for the liquid mixture extending from said flocculation chamber tothe bottom of said sedimentation trays to cause the liquid mixture fromthe flocculation chamber to flow through curtains of falling floc undersaid sedimentation trays and upwardly between the latter for thedeposition of sludge and the formation of a clarified liquid mixture,and a third enclosure forming a contact chamber arranged adjacent saidsedimentation trays for treating said clarified liquid mixture, saidcontact chamber being provided with an overflow for the effluent, saidsecond enclosure being provided with a sidewall having an upper endportion extending higher than said overflow, said sedimentation trayshaving upper ends which are lower then said upper end portion of saidsidewall whereby said liquid mixture is allowed to flow under gravityaction from said mixing chamber and over said upper ends, to saidoverflow, said first and second enclosures and said sedimentation traysbeing nested inside said contact chamber, and said first, second andthird enclosures having sidewalls constructed and arranged to Produce anup-and-down tortuous flow path, said first enclosure having a sidewallhaving an openended downwardly tapering bottom conical portion and anopen-ended upwardly tapering top conical portion, the side-wall of saidsecond enclosure having a funnel shape defining a conical hopper portionand a depending discharge tube portion extending into said bottomconical portion and opening adjacent the bottom thereof, a fourthenclosure surrounding said first enclosure and being conically shaped toform a sludge collector around said bottom conical portion, saidsedimentation trays being formed of downwardly tapering truncatedconical surfaces nested in radially spaced apart relationship one withinanother and relative to said conical hopper portion and above saidupwardly tapering top conical portion, an upright baffle plate beingfixed inside said third enclosure and arranged to form an upward flowpassage for said effluent leading from said contact chamber to saidoverflow, and a partition extending upwardly from the upper end of saidtop conical portion intermediate said conical hopper portion and saidsedimentation trays.
 4. A treatment plant for waste water as defined inclaim 3, further including a stirring impeller rotatably mounted intosaid conical hopper portion and arranged upon rotation to counterdownward flow therethrough; said recirculating means includes arecirculating and tumbling zone into said flocculation chamber, anairlift pump having a suction inlet positioned into the bottom of saidfourth enclosure and arranged to suck deposited sludge particles into asludge container above said flocculation chamber and a supernatantdischarge pipe connected to said sludge container and having an outletextending into said circulating and tumbling zone and arranged to feedsupernatant into said zone to cause recirculation of deposited sludgeparticles.